Usually, a polyoxyalkylene polyol or monool is obtained by using an alkali metal such as potassium hydroxide as a catalyst, and performing addition polymerization of an active hydrogen-containing compound with an alkylene oxide such as propylene oxide or ethylene oxide. In the addition polymerization of PO using an alkali metal catalyst, a low molecular weight monool as a by-product is formed by transfer of PO to allyl alcohol. This low molecular weight monool as a by-product has a problem that it causes a decrease in the number of functional groups of the polyoxyalkylene polyol and a urethane resin using such a polyol causes deterioration of mechanical properties. Therefore, there is known a method of using cesium hydroxide or double metal cyanide as a catalyst in order to decrease the amount of such a low molecular weight monool as a by-product to be formed (see, for example, Patent Documents 1 and 2).
On the other hand, in a polyoxyalkylene polyol obtained by addition polymerization of AO having 3 or more carbon atoms in the presence of the above-mentioned catalyst, a primary hydroxylation ratio of a terminal hydroxyl group is drastically low (for example, usually 2% or less when potassium hydroxide is used) and most terminal hydroxyl groups are secondary hydroxyl groups. Therefore, this polyol has insufficient reactivity as a polyol component of a thermosetting resin. For example, this polyol has low reactivity with an isocyanate group of an isocyanate group-containing compound (tolylene diisocyanate, etc.) and has insufficient reactivity as a polyol component of a urethane resin.
It is necessary to have a primary hydroxyl group as a terminal hydroxyl group so as to ensure sufficient reactivity with an isocyanate group. For this purpose, there is known a method in which a terminal hydroxyl group is converted into a primary hydroxyl group by further performing addition polymerization of a polyoxyalkylene polyol obtained by addition polymerization of AO having 3 or more carbon atoms with EO. However, since a polyethylene oxide moiety is hydrophilic, this method has a problem that hydrophobicity of the polyoxyalkylene polyol deteriorates and, when such a polyol is used, physical properties and the like of the urethane resin are largely changed by humidity. Therefore, there is known a method in which the amount of a primary hydroxyl group in a terminal hydroxyl group is increased by using a specific catalyst (see, for example, Patent Document 3).
It is also known to be possible to obtain a polyoxyalkylene polyol, in which reactivity with an isocyanate group is improved while decreasing the amount of a low molecular weight monool as a by-product to be formed, by performing addition polymerization of AO using a cesium hydroxide or double-metal cyanide catalyst, first, and then carrying out addition polymerization of AO using a specific catalyst (see, for example, Patent Document 4).